1. Field of the Invention
This invention relates to linear, saturated polyester compositions containing salts of salicylic acid as nucleating agents.
2. Description of the Prior Art
It is known to use nucleating agents in crystallizable polymers such as linear saturated polyesters of aromatic dicarboxylic acids. For example, it is known to use salts of certain hydrocarbon and polymeric carboxylic acids as nucleating agents for linear saturated polyester molding compositions.
A molding composition based on linear saturated polyester such as poly(ethylene terephthalate) should result in a molded product having good physical properties including flexural strength, modulus, tensile strength and impact properties. Further, the molding composition should have good molding properties including a fast molding cycle, a melt flow index for sufficient flow into the mold, good mold release properties and good finished appearance.
From a practical point of view, it is desirable that satisfactory properties, as outlined above, be attained using water heated molds. Water heated molds are heated to temperatures between 76.7.degree. C. (170.degree. F.) to about 100.degree. C. (212.degree. F.). In order to use water heated molds, it is desirable for crystallization to begin at as high a temperature as possible upon the cooling of the polyester melt which has been fed into the mold, and for the crystallizaion to continue during cooling to as low a temperature as possible. T.sub.cc is the temperature at which crystal formation begins. T.sub.ch is the temperature at which crystallization of the polyester melt ceases to occur upon cooling. It has been found that molded article appearance and mold release properties can be related to the T.sub.ch value. T.sub.ch is determined by measuring the temperature at which crystals appear upon heating a polyester composition in amorphous form. T.sub.cc and T.sub.ch can be measured using a Differential Scanning Calorimeter.